Combination stylet and sheath for an electrode array

ABSTRACT

A cochlear implant electrode assembly device ( 10 ) comprising an elongate electrode carrier member ( 11 ), a stiffening element ( 15 ), and a stiffening sheath ( 16 ) that at least partially envelops the elongate member ( 11 ). The member ( 11 ) is made of a resiliently flexible first material and has a plurality of electrodes ( 12 ) mounted thereon. The member ( 11 ) has a first configuration that allows it to be inserted into an implantee&#39;s cochlea ( 30 ). The member ( 11 ) also has a second configuration wherein the member is curved to match an inside surface of the cochlea ( 30 ), and at least one intermediate configuration between the first and second configurations. Both the stiffening element ( 15 ) and sheath ( 16 ) are made of a material that is relatively stiffer than the member ( 11 ). The stiffening element ( 15 ) and the stiffening sheath ( 16 ) in combination bias the elongate member ( 11 ) into the first configuration. If either the stiffening element ( 15 ) or the stiffening sheath ( 16 ) is removed or deactivated, the elongate member ( 11 ) adopts an intermediate configuration.

FIELD OF THE INVENTION

The present invention relates to an implantable device and, inparticular, to an implantable cochlear electrode assembly.

BACKGROUND OF THE INVENTION

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensorineural. Of these types, conductivehearing loss occurs where the normal mechanical pathways for sound toreach the hair cells in the cochlea are impeded, for example, by damageto the ossicles. Conductive hearing loss may often be helped by use ofconventional hearing aid systems, which amplify sound so that acousticinformation does reach the cochlea and the hair cells.

In many people who are profoundly deaf, however, the reason for deafnessis sensorineural hearing loss. This type of hearing loss is due to theabsence of, or destruction of, the hair cells in the cochlea whichtransduce acoustic signals into nerve impulses. These people are thusunable to derive suitable benefit from conventional hearing aid systems,because there is damage to or absence of the mechanism for nerveimpulses to be generated from sound in the normal manner.

It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.U.S. Pat. No. 4,532,930, the contents of which are incorporated hereinby reference, provides a description of one type of traditional cochlearimplant system.

Cochlear implant systems have typically consisted of two key components,namely an external component commonly referred to as a processor unit,and an implanted internal component commonly referred to as astimulator/receiver unit. Traditionally, both of these components havecooperated together to provide the sound sensation to an implantee.

The external component has traditionally consisted of a microphone fordetecting sounds, such as speech and environmental sounds, a speechprocessor that converts the detected sounds and particularly speech intoa coded signal, a power source such as a battery, and an externalantenna transmitter coil.

The coded signal output by the speech processor is transmittedtranscutaneously to the implanted stimulator/receiver unit situatedwithin a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs through use of an inductive couplingprovided between the external antenna transmitter coil which ispositioned to communicate with an implanted antenna receiver coilprovided with the stimulator/receiver unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedstimulator/receiver unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

The implanted stimulator/receiver unit typically included the antennareceiver coil that receives the coded signal and power from the externalprocessor component, and a stimulator that processes the coded signaland outputs a stimulation signal to an intracochlea electrode assemblywhich applies the electrical stimulation directly to the auditory nerveproducing a hearing sensation corresponding to the original detectedsound.

The external componentry of the cochlear implant has been traditionallycarried on the body of the implantee, such as in a pocket of theimplantee's clothing, a belt pouch or in a harness, while the microphonehas been mounted on a clip mounted behind the ear or on a clothing lapelof the implantee.

More recently, due in the main to improvements in technology, thephysical dimensions of the speech processor have been able to be reducedallowing for the external componentry to be housed in a small unitcapable of being worn behind the ear of the implantee. This unit hasallowed the microphone, power unit and the speech processor to be housedin a single unit capable of being discretely worn behind the ear, withthe external transmitter coil still positioned on the side of the user'shead to allow for the transmission of the coded sound signal from thespeech processor and power to the implanted stimulator unit.

Together with improvements in available technology much research hasbeen undertaken in the area of understanding the way sound is naturallyprocessed by the human auditory system. With such an increasedunderstanding of how the cochlea naturally processes sounds of varyingfrequency and magnitude, there is a need to provide an improved cochlearimplant system that delivers electrical stimulation to the auditorynerve in a way that takes into account the natural characteristics ofthe cochlea.

It is known in the art that the cochlea is tonotopically mapped. Inother words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea is exploited by providing the electrode assemblywith an array of electrodes, each electrode being arranged andconstructed to deliver a cochlea-stimulating signal within a preselectedfrequency range to the appropriate cochlea region. The electricalcurrents and electric fields from each electrode stimulate the ciliadisposed on the modiola of the cochlea. Several electrodes may be activesimultaneously.

It has been found that in order for these electrodes to be effective,the magnitude of the currents flowing from these electrodes and theintensity of the corresponding electric fields, are a function of thedistance between the electrodes and the modiola. If this distance isrelatively great, the threshold current magnitude must be larger than ifthe distance is relatively small. Moreover, the current from eachelectrode may flow in all directions, and the electrical fieldscorresponding to adjacent electrodes may overlap, thereby causingcross-electrode interference. In order to reduce the thresholdstimulation amplitude and to eliminate cross-electrode interference, itis advisable to keep the distance between the electrode array and themodiola as small as possible. This is best accomplished by providing theelectrode array in the shape which generally follows the shape of themodiola. Also, this way the delivery of the electrical stimulation tothe auditory nerve is most effective as the electrode contacts are asclose to the auditory nerves that are particularly responsive toselected pitches of sound waves.

In order to achieve this electrode array position close to the insidewall of the cochlea, the electrode needs to be designed in such a waythat it assumes this position upon or immediately following insertioninto the cochlea. This is a challenge as the array needs to be shapedsuch that it assumes a curved shape to conform with the shape of themodiola and must also be shaped such that the insertion process causesminimal trauma to the sensitive structures of the cochlea. In this senseit has been found to be desirable for the electrode array be generallystraight during the insertion procedure.

Several procedures have been adopted to provide an electrode assemblythat is relatively straightforward to insert while adopting a curvedconfiguration following insertion in the cochlea. In one case, aplatinum wire stylet is used to hold a pre-curved electrode array in agenerally straight configuration up until insertion. Followinginsertion, the platinum stylet is withdrawn allowing the array to returnto its pre-curved configuration. While such an arrangement has provedbeneficial, penetration of the wall of the cochlea is possible if thesurgeon does not insert the array using an appropriate rate andorientation, or withdraw the stylet at the appropriate end point duringinsertion of the assembly.

In another development, a bimetallic filament (such as nickel/titanium)or a shape memory alloy (eg. an alloy of nickel and titanium) ispositioned in the electrode assembly and used to again hold a pre-curvedelectrode array in a generally straight configuration while the array isat about room temperature. On insertion into the body and exposure tobody temperature, the alloy or filament bends into a pre-selected curvedconfiguration.

In a still further arrangement, a longitudinal element that is arrangedon one side of the array and constructed to change its dimension oninsertion can be utilised. For example, the longitudinal element couldinclude a hydrogel, such as polyacrylic acid (PAA) or polyvinyl alcohol(PVA), which expands after insertion by absorbing water from thecochlear fluid.

In developing such electrode array designs, it is of great importancethat the design be constructed to minimise potential damage to sensitivestructures in the cochlear on insertion and placement. For example, inthe case of use of platinum stylets, some studies suggest that wallpenetration is a problem in about 20% of cases. Each of the aboveconstructions suffer from a number of disadvantages in this regard.

The present invention is directed to an electrode assembly adapted toovercome some of the difficulties of prior art electrode assemblies.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

According to a first aspect, the present invention is an implantabletissue-stimulating device comprising:

-   -   an elongate member having a plurality of electrodes mounted        thereon and having a first configuration that allows said member        to be inserted into an implantee's body, a second configuration        wherein said elongate member is adapted to apply a preselected        tissue stimulation with the electrodes, and at least one        intermediate configuration between said first and second        configurations, said elongate member being made of a resiliently        flexible first material;    -   a stiffening element made of a material relatively stiffer than        said first material; and    -   a stiffening sheath at least partially enveloping said elongate        member and made of a material relatively stiffer than said first        material;    -   wherein said stiffening element and said stiffening sheath in        combination bias said elongate member into said first        configuration and further wherein if either the stiffening        element or the stiffening sheath is removed or deactivated, the        elongate member adopts said at least one intermediate        configuration.

In a preferred embodiment, the second configuration of the elongatemember is curved. More preferably, the elongate member adopts a spiralconfiguration when in the second configuration.

According to a second aspect, the present invention is a cochlearimplant electrode assembly including:

-   -   an elongate electrode carrier member having a plurality of        electrodes mounted thereon and having a first configuration that        allows said member to be inserted into an implantee's cochlea, a        second configuration wherein said elongate member is curved to        match an inside surface of said cochlea, and at least one        intermediate configuration between said first and second        configurations, said elongate member being made of a resiliently        flexible first material;    -   a stiffening element made of a material relatively stiffer than        said first material; and    -   a stiffening sheath at least partially enveloping said elongate        member and made of a third material relatively stiffer than said        first material;    -   wherein said stiffening element and said stiffening sheath in        combination bias said elongate member into said first        configuration and further wherein if either the stiffening        element or the stiffening sheath is removed or deactivated, the        elongate member adopts said at least one intermediate        configuration.

The elongate member is preferably preformed from a plastics materialwith memory and is preformed to the second configuration. The elongatemember preferably has a first end that is firstly inserted into theimplantee.

In a preferred embodiment, the first configuration is preferablysubstantially straight. More preferably, the first configuration isstraight.

In a preferred embodiment, the elongate member is formed from a suitablebiocompatible material. In one embodiment, the material can be asilicone, such as a flexible silicone elastomer—Silastic. Silastic MDX4-4210 is an example of one suitable silicone for use in the formationof the elongate member. In another embodiment, the elongate member canbe formed from a polyurethane.

In a further embodiment, the elongate member can have a resilientlyflexible tip member extending forwardly from the first end of the body.The tip member preferably has a distal end and a proximal end. The tipmember can have a stiffness that is relatively less stiff than saidstiffening element. The tip member can further be formed of a materialthat is substantially the same or the same stiffness as the body of theelongate member. In another embodiment, the tip member can be formed ofa material that is relatively less stiff than at least a portion of theelongate member. In a further embodiment, the tip member can be formedof a material that undergoes a change in stiffness, preferably adecrease in stiffness, on insertion into the body, such as the cochlea.

In a further embodiment, the stiffness of the tip member can vary alongat least a portion of its length from its distal end to its proximalend. In one embodiment, the stiffness of the tip member can vary overthe entire length of the tip member or only a portion thereof. Thestiffness can increase from the distal end to the proximal end. In oneembodiment, the stiffness of the tip member over said portion or itslength can increase gradually from its distal end towards to theproximal end. The increase in stiffness can be substantially smooth orincrease in a stepwise fashion.

In a further embodiment, the tip member can be formed of the samematerial as the body of the elongate member. In another embodiment, thetip member can be formed of a different material to that of the body ofthe elongate member. The tip member can be comprised of an innerrelatively stiff core of material having a tapered end, with at leastthe tapered end being overlaid by a relatively flexible material thatextends beyond the tapered end of the core material so that the tipmember undergoes a gradual decrease in flexibility in the region of thetapered end of the core moving away from the distal end.

The tip member can be formed separately to the body of the elongatemember and mounted thereto. For example, the tip member can be adheredto the first end of the body of the elongate member. In anotherembodiment, the tip member can be integrally formed with the body of theelongate member. The tip member can be formed from a silicone material.In another embodiment, the tip member can be formed of an elastomericmaterial, such as polyurethane.

In another embodiment, the tip member can have a plurality of metallicparticles dispersed therethrough. The metallic particles can besubstantially evenly dispersed through the tip member. Alternatively,the metallic particles can be non-evenly dispersed throughout the tipmember. In one embodiment, the metallic particles can increase indensity away from the distal end towards the proximal end of the tipmember. By varying the density of the metallic particles, it is possibleto vary the relative stiffness of the tip member.

The metallic particles preferably comprise a biocompatible material,such as platinum. The particles can be substantially spherical orspherical. It will be appreciated that the particles can have othersuitable shapes. In one embodiment, the particles can have a diameterbetween about 50 μm and 100 μm.

In addition to, or instead of, being used to potentially modify thephysical characteristics of the tip member, the provision of themetallic particles also result in the tip member being detectable byfluoroscopy and X-ray techniques. This provides another means for thesurgeon to monitor the placement and position of the tip member duringor after insertion of the electrode array in the body, such as in thecochlea.

When the elongate member is in the first configuration, the tip memberis preferably substantially straight and, more preferably, straight.

In a further embodiment, the tip member can be coated with a lubriciousmaterial. The lubricious material can be a bioresorbable ornon-bioresorbable material.

The tip member can be formed from, or incorporate as a portion thereof,a bioresorbable material. The presence of the bioresorbable materialpreferably results in the flexibility of the tip member increasing oninsertion of the tip member into the body, such as the cochlea. Thebioresorbable material in the tip member can be selected from the groupconsisting of polyacrylic acid (PAA), polyvinyl alcohol (PVA),polylactic acid (PLA) and polyglycolic acid (PGA).

In another embodiment, the tip member can be formed from, or incorporateas a portion thereof, a polymeric coating which becomes softer, and soincreases in resilient flexibility, in the presence of moisture or bodyheat.

The tip member preferably has a length from its distal end to itsproximal end in the range of about 0.3 to 4 mm, more preferably about1.0 to 3 mm. The diameter of the tip member can be substantiallyconstant for a majority of its length or can vary in diameter. The tipmember can be substantially cylindrical, cylindrical, or non-cylindricalfor a majority of its length. At the distal end, the diameter preferablygradually decreases to form a rounded end. The maximum diameter of thetip member is preferably about 0.55 mm.

In one embodiment, the tip member can be solid. In another embodiment,the tip member can have an external wall defining a cavity. In oneembodiment, the cavity can have a diameter greater than that of thereceiving portion of the body of the elongate member. In a furtherembodiment, the cavity can extend from the proximal end towards thedistal end of the tip member. The cavity can decrease in diameter awayfrom the proximal end. The cavity can be in communication with a distalend of the receiving portion of the body of the elongate member. In afurther embodiment, the stiffening means can extend into the cavity whenpositioned within the device or assembly according to the respectiveaspects of the present invention. In a preferred embodiment, the tipmember can move relative to the stiffening means when it extends intothe cavity of the tip member.

In general, the tip could be made of a combination of materials arrangedin a variety of geometries depending on the specific design goal. Theoutside shape and size of the tip can also be made in a variety of formsdepending on the design goal.

In one embodiment, the stiffening element is formed of a bioresorbablematerial which softens or dissolves on exposure to a fluid. Thestiffening element can soften or dissolve on exposure to a salinesolution or a body fluid of the implantee, such as cochlear fluid.

In a further embodiment, the bioresorbable material of the stiffeningelement is selected from the group consisting of polyacrylic acid (PAA),polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolic acid(PGA). It is envisaged that other similar materials could also be used.

In another embodiment, the stiffening element can be formed from anon-bioresorbable material. In this embodiment, the stiffening elementcan comprise a metallic stylet, or a stylet from any other suitablestiffening material, extending through a lumen in the elongate member.In one embodiment, the stylet can be formed from a biocompatiblematerial, such as a metal, metallic alloy or a stiff plastic. In apreferred embodiment, a metal stylet can be formed from platinum.

In a still further embodiment, the stiffening element can be formed froma shape memory alloy or a heat sensitive material. For example, thestiffening element can be formed from a nickel/titanium alloy, or abimetallic element formed of a laminate of two different metals, that isshaped to take a straight or substantially straight configuration atroom temperature but bends into another shape once it is exposed to bodytemperature.

In one embodiment, the lumen for the stylet can be cylindrical and alsocan have an opening formed therein. In the case of a metal stylet, thestylet can extend out of the opening allowing the stylet to bemanipulated and removed from the lumen during or following insertion ofthe device. In the case of a bibresorbable stiffening element, theopening can act as a fluid ingress means allowing body fluids to enterthe lumen on insertion of the device into an implantee.

Where the stiffening element is a metallic or metallic alloy or plasticstylet, the stiffening sheath is preferably formed of a bioresorbablematerial which dissolves or softens on exposure to a fluid. Thestiffening sheath can dissolve or soften on exposure to a salinesolution or a body fluid of the implantee, such as cochlear fluid.

In a further embodiment, the bioresorbable material of the stiffeningsheath is selected from the group consisting of polyacrylic acid (PAA),polyvinyl alcohol (PVA), polylactic acid (PLA) and polyglycolic acid(PGA). It is also envisaged that other suitable materials could also beused.

The device can include an additional layer surrounding the stiffeningsheath. The additional layer can have a first rate of fluid ingresstherethrough and have at least one fluid ingress means formed therein,the rate of fluid ingress through the fluid ingress means being greaterthan the first rate of fluid ingress through the additional layer.

The fluid ingress means can comprise one or more openings in theadditional layer. The openings can be closable. The openings cancomprise slits in the additional layer. The slits can be formed to allowsubstantially the same or the same rate of ingress of fluid through theadditional layer. In another embodiment, at least one slit can allow adifferent rate of progress of fluid through the additional layercompared to the other slits.

Where the stiffening element is a metal or bioresorbable stylet, thestiffening sheath can, in one embodiment, be formed from a shape memoryalloy or a heat sensitive material. For example, the stiffening sheathcan be formed from a nickel/titanium alloy, or a bimetallic elementformed of a laminate of two different metals, that is shaped to take andmaintain the straight or substantially straight configuration of theelongate member at room temperature but bends it into another shape onceit is exposed to body temperature.

While both the stiffening element and the stiffening sheath are inposition within the device, it will retain the first configuration,which as discussed is preferably straight. If the stiffening sheath isremoved or softened, whether it is by dissolution or otherwise, theremaining stiffening element has insufficient strength to retain theelongate member in its first configuration. It is preferred that theelongate member, on removal or softening of the stiffening sheath, willadopt an intermediate configuration in which the elongate member has atleast some curvature.

The purpose of allowing the elongate member to adopt this intermediateconfiguration is to enable the elongate member to be inserted into thecochlea in a way which minimises trauma to the walls of the cochlea. Thepreferred shape of this intermediate configuration is for the elongatemember to assume a shape that is more curved than the straightconfiguration present upon insertion. By providing the previouslystraight array with a more curved shape, the elongate member is guidedto adopt a mid-scala trajectory as it is inserted into the cochlea. Thisensures that as the elongate member is carefully inserted deeper intothe spiral shaped cochlea, the intermediate curved configuration assistsin assuring that the elongate member can be inserted deep into thecochlea without causing excessive trauma to the walls of the cochlea.

On subsequent removal of the stiffening element, the elongate member isfree to adopt the fully curved second configuration desired of animplant for final position in the cochlea.

The present invention provides a surgeon with a means to at leastpartially control the rate of curvature formation in a cochlearelectrode assembly during insertion into the cochlea. Such increasedcontrol is envisaged to reduce the potential for trauma to the cochleacaused by electrode assembly insertion. The present invention alsoprovides a means of assisting the insertion process of the electrodeassembly into the cochlea by allowing the electrode assembly to alterits configuration during the insertion process to allow for deeper andmore desirable cochlea penetration.

In a further embodiment, at least a portion of an outer surface of theelongate member can have a coating of a lubricious material. In oneembodiment, a substantial portion or the entire outer surface of theelongate member can have a coating of the lubricious material.

In this embodiment, the lubricious material can be selected from thegroup comprising polyacrylic acid (PAA), polyvinyl alcohol (PVA),polylactic acid (PLA) and polyglycolic acid (PGA). It is envisaged thatother similar materials could also be used.

In a further aspect, the present invention comprises a method ofimplanting a tissue-stimulating device or cochlear electrode assemblydevice as defined herein in a body of an implantee.

In this aspect, the method can comprise a step of accessing theimplantation site and then a step of inserting the device. Prior toinsertion, the device is preferably substantially straight or straight.On insertion, the device can adopt an intermediate configuration (asdefined herein). Either prior to full insertion or following fullinsertion, the device preferably adopts its second configuration.

Once implanted, the electrodes can receive stimulation signals from astimulator means. The stimulator means is preferably electricallyconnected to the elongate member by way of an electrical lead. The leadcan include the one or more wires extending from each electrode of thearray mounted on the elongate member.

In one embodiment, the lead can extend from the elongate member to thestimulator means or at least the housing thereof. In one embodiment, thelead is continuous with no electrical connectors, at least external thehousing. of the stimulator means, required to connect the wiresextending from the electrodes to the stimulator means. One advantage ofthis arrangement is that there is no requirement for the surgeonimplanting the device to make the necessary electrical connectionbetween the wires extending from the electrodes and the stimulatormeans.

The stimulator means is preferably positioned within a housing that isimplantable within the implanted. The housing for the stimulator meansis preferably implantable within the bony well in the bone behind theear posterior to the mastoid.

When implantable, the housing preferably contains, in addition to thestimulator means, a receiver means. The receiver means is preferablyadapted to receive signals from a controller means. The controller meansis, in use, preferably mounted external to the body of the implanteesuch that the signals are transmitted transcutaneously through theimplantee.

Signals can preferably travel from the controller means to the receivermeans and vice versa. The receiver means can include a receiver coiladapted to receive radio frequency (RF) signals from a correspondingtransmitter coil worn externally of the body. The radio frequencysignals can comprise frequency modulated (FM) signals. While describedas a receiver coil, the receiver coil can preferably transmit signals tothe transmitter coil which receives the signals.

The transmitter coil is preferably held in position adjacent theimplanted location of the receiver coil by way of respective attractivemagnets mounted centrally in, or at some other position relative to, thecoils.

The external controller can comprise a speech processor adapted toreceive signals output by a microphone. During use, the microphone ispreferably worn on the pinna of the implantee, however, other suitablelocations can be envisaged, such as a lapel of the implantee's clothing.The speech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for cochlear implant systems. The encodedsequence is transferred to the implanted stimulator/receiver means usingthe transmitter and receiver coils. The implanted stimulator/receivermeans demodulates the FM signals and allocates the electrical pulses tothe appropriate attached electrode by an algorithm which is consistentwith the chosen speech coding strategy.

The external controller further comprises a power supply. The powersupply can comprise one or more rechargeable batteries. The transmitterand receiver coils are used to provide power via transcutaneousinduction to the implanted stimulator/receiver means and the electrodearray.

While the implant system can rely on external componentry, in anotherembodiment, the controller means, including the microphone, speechprocessor and power supply can also be implantable. In this embodiment,the controller means can be contained within a hermetically sealedhousing or the housing used for the stimulator means.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, preferred embodiments of the invention are nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a simplified cross-sectional view of one embodiment of anelectrode assembly according to the present invention depicted in itsfirst configuration;

FIG. 2 is a simplified side elevational view of the electrode assemblyof FIG. 1 depicted in an intermediate configuration;

FIG. 3 is a simplified part-sectional, part side elevational view of theelectrode assembly depicted in its second configuration followinginsertion in the cochlea;

FIG. 4 is a simplified cross-sectional view of another embodiment of anelectrode assembly according to the present invention; and

FIGS. 5 a-5 d depict alternative tip structures for the electrodeassembly depicted in FIG. 4.

PREFERRED MODE OF CARRYING OUT THE INVENTION

One embodiment of a cochlear implant electrode assembly according to thepresent invention is depicted generally as 10 in the drawings.

The depicted electrode assembly 10 has an electrical lead extending backto a stimulator/receiver housing. In considering this invention, it isto be understood that each electrode may have one or more wires (notdepicted) electrically connected thereto and extending from eachrespective electrode back through the lead to the stimulator/receiver.

The assembly 10 comprises an elongate electrode carrier member 11 havinga plurality of electrodes 12 mounted thereon. For the purposes ofclarity, the electrodes 12 depicted in FIG. 1 are not necessarily shownto scale.

The depicted elongate member 11 is preformed from a resiliently flexiblesilicone with memory and is preformed to a curved configuration suitablefor insertion in the scala tympani of the cochlea. The elongate member11 has a first end 13 that is firstly inserted into the cochlea uponinsertion of the assembly 10.

As depicted in FIG. 4, the elongate member 11 can have a tip member 29integrally formed with its first end 13. The tip 29 is formed from thesame silicone used to fabricate the elongate member 11 and, in thedepicted embodiment, the material of tip member 29 has a resilientflexibility equal to that of the material used for the carrier member11.

Possible alternative constructions for the tip member 29 are provided inFIGS. 5 a-5 d. As depicted in FIG. 5 a, the tip member 70 can be solidand formed of an inner core 71 of relatively stiff material 71 and anouter layer 72 of relatively flexible material. The core 71 can taper indiameter over region 73 towards the distal end 21. The taper 73 causesthe overall stiffness of the tip 70 to increase over the length of thetaper 73 away from the distal end 21. The outer layer 72 can be formedof the same material as the remainder of the body of the elongatecarrier member 11 or can be a different material.

As depicted in FIG. 5 b, the tip member 40 can comprise a solid massintegrally formed to the first end 13 of the elongate carrier 11.

Still further and as depicted in FIG. 5 c, the tip member 50 cancomprise a solid mass 51 that is formed separately from the carriermember 11 and subsequently adhered thereto.

As depicted in FIG. 5 d, the tip member 60 can comprise an elastomericsilicone material having a plurality of substantially spherical platinumparticles 61 dispersed therethrough. The particles 61 have a diameterbetween about 50 μm and 100 μm. It will be appreciated that theparticles 61 depicted in FIG. 6 d are not drawn to scale.

In FIG. 5 d, the particles 61 are depicted as substantially evenlydispersed through the tip member 60. In another embodiment, theparticles could be non-evenly dispersed through the tip member. Forexample, the particles could increase in density away from the distalend 21 towards the proximal end of the tip member 60. By varying thedensity of the platinum particles 61, it is possible to vary therelative stiffness of the tip member 60.

In addition to, or instead of, being used to potentially modify thephysical characteristics of the tip member, the provision of themetallic particles 61 also result in the tip member 60 being detectableby fluoroscopy and X-ray techniques. This provides another means for thesurgeon to either monitor the placement and position of the tip member60 during or after insertion of the electrode array 10 in an implantee'scochlea.

Disposed within a lumen 14 is a substantially straight platinum stylet15. The stylet 15 alone has a stiffness that is insufficient to retainthe silicone elongate member 11 in a straight configuration.

While a platinum stylet is depicted, a bioresorbable stylet formed froma bioresorbable polyacrylic acid (PAA) that is adapted to dissolve orsoften on exposure to cochlear fluids could be utilised with appropriatemodification to the elongate carrier member 11. Equally, whilst asubstantially cylindrical lumen is depicted, the lumen 14 could indeedbe any shape necessary to perform the function. Again, the PAA stylet inthis invention has a stiffness insufficient to retain the siliconeelongate member 11 in a straight configuration as depicted in FIG. 1. Itwill be appreciated that a bioresorbable stylet could be formed fromother suitable bioresorbable materials. A stylet made from a shapememory alloy or heat sensitive material could also be utilised as astylet 15.

Overlaying the depicted elongate member 11 is a stiffening sheath 16 ofbioresorbable material. The bioresorbable material of the depictedstiffening sheath 16 is PAA that is adapted to dissolve on exposure tocochlear fluids. Other suitable bioresorbable materials can be envisagedand such materials need not necessarily dissolve on exposure to fluids,the current invention could also function correctly if the sheath 16 ismade of a material that softens upon exposure to fluids but does not getabsorbed.

While the elongate member 11 is manufactured with a preformed curvedconfiguration, the assembly 10 is typically delivered to a surgeon withthe stylet 15 and sheath 16 in place. The combination of the stylet 15and sheath 16 is sufficient to hold the elongate member 11 in thestraight configuration depicted in FIG. 1.

On insertion into the scala tympani of the cochlea 30, the cochlearfluids commence to dissolve or soften the sheath 16. As the PAA softensand dissolves, the elongate member 11 commences to re-curl (see FIG. 2)as the stiffness of the stylet 15 is insufficient to hold the elongatemember 11 straight. The provision of the stylet 15 within the elongatemember 11 does, however, prevent the elongate member 11 from adoptingits pre-formed spirally curved configuration.

As the elongate member 11 curls, the surgeon can continue to furtherinsert the assembly 10 into the scala tympani 31 with a lessened risk ofthe member 11 puncturing fine tissues of the cochlea 30. It is possiblethat during the further insertion process the surgeon may simultaneouslywithdraw the platinum stylet 15 through the opening 17 of the lumen 14at end 18. On withdrawal of the stylet 15, the elongate member 11 isfree to adopt the spiral configuration depicted in FIG. 3 with theelectrodes facing the modiola within the cochlea 30 so that they arepositioned as close as possible to the spiral ganglia thereof.

It is also envisaged that in one arrangement the surgeon may withdrawthe stylet 15 first and rely upon the sheath 16 to maintain the array inthe intermediate position.

The combination of the stiffening element 15 and stiffening sheath 16provides the surgeon with greater control of the implantation procedurefor the cochlear implant electrode assembly 10. The provision of greatercontrol minimises the potential for trauma to the sensitive tissuesinside the cochlea and also enhances the likelihood of successfulplacement of the assembly 10 at the first attempt.

While the preferred embodiment of the invention has been described inconjunction with a cochlear implant, it is to be understood that thepresent invention has wider application to other implantable electrodes,such as electrodes used with pacemakers.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1-27. (canceled)
 28. A method for inserting an electrode array into acochlea comprising the steps of: stiffening an elongate member in afirst configuration using a first and second biasing means, wherein theelongate member has a plurality of electrodes mounted thereon and theelongated member is made from a memory material capable of a secondconfiguration; modifying the first biasing means while inserting theelongate member into the cochlea; and removing the second biasing meansfrom the elongate member such that the elongate member assumes thesecond configuration when insertion into the cochlea is completed. 29.The method of claim 28, further comprising the step of positioning theelongate member during insertion to apply preselected tissue stimulationwith the plurality of electrodes.
 30. The method of claim 28, whereinthe first configuration is substantially straight.
 31. The method ofclaim 28, wherein the second configuration is curved.
 32. The method ofclaim 28, wherein the first biasing means is least partially envelopesthe elongate member.
 33. The method of claim 32, wherein the firstbiasing means is a sheath.
 34. The method of claim 28, wherein modifyingthe first biasing means comprises dissolving the first biasing means.35. The method of claim 28, wherein modifying the first biasing meanscomprises deactivating the first biasing means.
 36. The method of claim28, wherein modifying the first biasing means comprises bending thefirst biasing means using heat.
 37. The method of claim 36, wherein thefirst biasing means is made from a heat sensitive material.
 38. Themethod of claim 28, wherein the second biasing means is a styletpartially in a lumen of the elongate member.
 39. The method of claim 28,wherein the first biasing means is modified before the second biasingmeans is removed.
 40. The method of claim 28, further comprising thestep of inserting the elongated member into the cochlea when theelongated member is in the first configuration.
 41. The method of claim28, wherein the elongated member may be partially outside the cochleawhen insertion into the cochlea is completed.
 42. An electrode array foran implantable hearing prosthesis comprising: an elongate member havinga plurality of electrodes mounted thereon made from a resilientlyflexible material; a tip region mounted on a distal end of the elongatemember, the tip region made from one or more materials that collectivelyare relatively less stiff than the elongate member; and a stiffeningsheath that surrounds the tip region, wherein the stiffening sheath is amaterial that is relatively stiffer than the tip region.
 43. Theelectrode array of claim 42, wherein the stiffening sheath dissolvesupon insertion into a cochlea.
 44. The electrode array of claim 42,wherein the tip region comprises metallic particles.
 45. The electrodearray of claim 44, wherein the metallic particles are denser towards aproximal end of the tip region than the distal end of the tip region.46. The electrode array of claim 44, wherein the metallic particles varythroughout the tip region.
 47. The electrode array of claim 42, whereinthe tip region is detachable from the elongate member.
 48. The electrodearray of claim 42, wherein the tip region tapers towards a distal end.49. The electrode array of claim 42, further comprising a stiffeningelement inserted into a lumen of the elongate member.
 50. An electrodearray for an implantable hearing prosthesis comprising: an elongatemember having a plurality of electrodes mounted thereon and having afirst configuration that allows the elongate member to be inserted intoan implantee's body, a second configuration wherein the elongate memberis adapted to apply preselected tissue stimulation with the electrodes,and at least one intermediate configuration between the first and secondconfigurations; a stiffening element at least partially inserted in alumen of the elongate member; and a stiffening sheath at least partiallyenveloping the elongate member; wherein the stiffening element and thestiffening sheath in combination bias the elongate member into the firstconfiguration and further wherein either the stiffening element or thestiffening sheath is used alone to bias the elongate member into the atleast one intermediate configuration.
 51. The electrode array of claim50, wherein the second configuration is curved.
 52. The electrode arrayof claim 50, wherein the first configuration is substantially straight.53. The electrode array of claim 50, wherein the stiffening element isremoved from the lumen thereby allowing the stiffening sheath to biasthe elongate member into the at least one intermediate configuration.54. The electrode array of claim 53, wherein the stiffening sheath isremoved to allow the elongate member to adopt the second configurationwhen inserted in the cochlea.
 55. The electrode array of claim 53,wherein the stiffening sheath dissolves to allow the elongate member toadopt the second configuration when inserted in the cochlea.
 56. Theelectrode array of claim 53, wherein the stiffening sheath bends toallow the elongate member to adopt the second configuration wheninserted in the cochlea.
 57. The electrode array of claim 50, whereinthe stiffening element dissolves in the lumen thereby allowing thestiffening sheath to bias the elongate member into the at least oneintermediate configuration.
 58. The electrode array of claim 57, whereinthe stiffening sheath is removed to allow the elongate member to adoptthe second configuration when inserted in the cochlea.
 59. The electrodearray of claim 57, wherein the stiffening sheath dissolves to allow theelongate member to adopt the second configuration when inserted in thecochlea.
 60. The electrode array of claim 57, wherein the stiffeningsheath bends to allow the elongate member to adopt the secondconfiguration when inserted in the cochlea.
 61. The electrode array ofclaim 50, wherein the stiffening element bends in the lumen therebyallowing the stiffening sheath to bias the elongate member into the atleast one intermediate configuration.
 62. The electrode array of claim61, wherein the stiffening sheath is removed to allow the elongatemember to adopt the second configuration when inserted in the cochlea.63. The electrode array of claim 61, wherein the stiffening sheathdissolves to allow the elongate member to adopt the second configurationwhen inserted in the cochlea.
 64. The electrode array of claim 61,wherein the stiffening sheath bends to allow the elongate member toadopt the second configuration when inserted in the cochlea.
 65. Theelectrode array of claim 50, wherein the stiffening sheath is removedfrom the elongate member thereby allowing the stiffening element to biasthe elongate member into the at least one intermediate configuration.66. The electrode array of claim 65, wherein the stiffening element isremoved from the lumen to allow the elongate member to adopt the secondconfiguration when inserted in the cochlea.
 67. The electrode array ofclaim 65, wherein the stiffening element dissolves in the lumen to allowthe elongate member to adopt the second configuration when inserted inthe cochlea.
 68. The electrode array of claim 65, wherein the stiffeningelement bends in the lumen to allow the elongate member to adopt thesecond configuration when inserted in the cochlea.
 69. The electrodearray of claim 50, wherein the stiffening sheath dissolves therebyallowing the stiffening sheath to bias the elongate member into the atleast one intermediate configuration.
 70. The electrode array of claim69, wherein the stiffening element is removed from the lumen to allowthe elongate member to adopt the second configuration when inserted inthe cochlea.
 71. The electrode array of claim 69, wherein the stiffeningelement dissolves in the lumen to allow the elongate member to adopt thesecond configuration when inserted in the cochlea.
 72. The electrodearray of claim 69, wherein the stiffening element bends in the lumen toallow the elongate member to adopt the second configuration wheninserted in the cochlea.
 73. The electrode array of claim 50, whereinthe stiffening sheath bends thereby allowing the stiffening sheath tobias the elongate member into the at least one intermediateconfiguration.
 74. The electrode array of claim 73, wherein thestiffening element is removed from the lumen to allow the elongatemember to adopt the second configuration when inserted in the cochlea.75. The electrode array of claim 73, wherein the stiffening elementdissolves in the lumen to allow the elongate member to adopt the secondconfiguration when inserted in the cochlea.
 76. The electrode array ofclaim 73, wherein the stiffening element bends in the lumen to allow theelongate member to adopt the second configuration when inserted in thecochlea.
 77. The electrode array of claim 50, wherein the elongatemember is made from a material having a memory shape of the secondconfiguration.